Conventionally, in mobile communication systems, communications have been performed in multiple access schemes where a plurality of mobile stations is simultaneously connected to a single base station in a cell to perform radio communications. In recent years, more increases in speed and capacity in data communications have been demanded in such multiple access schemes, and studies in this field have actively been performed.
As one of methods of achieving increases incapacity, considered is efficient packet scheduling in the base station. As one of such methods, proposed is a method of scheduling packets efficiently based on information of propagation path conditions from each mobile station. In High Speed Downlink Packet Access (HSDPA) in the W-CDMA (Wideband Code Division Multiple Access) mobile communication system, such a method has been proposed that the mobile station reports CQI (Channel Quality Indicator) that is propagation path condition information of downlink radio communication to the base station, and that the base station performs scheduling of packets based on the CQI reported from each mobile station.
Currently, 3GPP (3rd Generation Partnership Project) has studies one-cell reuse OFDM(TDMA,FDMA) (Orthogonal Frequency Division Multiplex/Time Division Multiple Access, Frequency Division Multiple Access) communication schemes by adopting the OFDM (Orthogonal Frequency Division Multiplex) communication scheme that is one of multicarrier communication schemes in the downlink radio communication scheme in order to develop a standard of the next-generation communication system. This communication scheme is of technique where in a multi-cell environment comprised of a plurality of cells, communications are performed using the same frequencies in all the cells, and in communicating, the modulation scheme is OFDM, while TDMA/FDMA is used as the access scheme.
OFDM, TDMA and FDMA will briefly be described below which are elemental techniques of the OFDM/(TDMA, FDMA) communication scheme.
First, the OFDM communication scheme is a scheme adopted also in the 5 GHz-band wireless LAN (Local Area Network) system, where tens to thousands of carries are allocated at minimum frequency intervals that do not cause interference in theory to enable simultaneous communications. Generally, in the OFDM communication scheme, this carrier is referred to as a subcarrier, and each subcarrier is modulated with a modulation scheme such as QPSK (Quadrature Phase Shift keying), 16QAM (Quadrature Amplitude Modulation), 64QAM or the like to perform communications.
Next, the TDMA communication scheme is a scheme where in transmitting and receiving the data, the time is divided and each mobile station performs radio communications. Generally, in the communication system using TDMA in the access scheme, used is a frame structure having a plurality of slots each of which is a unit time to communicate.
Next, the FDMA communication scheme is a scheme where frequencies are divided for accesses in transmitting and receiving the data. Generally, in the communication system using FDMA in the access scheme, frequencies are divided into some bands to separate frequency bands to gain access, and the scheme thereby distinguishes between mobile stations that perform radio communications.
Next, an explanation is given about OFDM/(TDMA, FDMA) based on the aforementioned introductory descriptions. FIG. 10 is a diagram showing an example of a two-dimensional frame structure of OFDM/(TDMA, FDMA). In FIG. 10, the vertical axis represents the frequency, and the horizontal axis represents the time. A single rectangle is a minimum unit used in data transmission, and in this description, referred to as a slot, while a plurality of slots periodically arranged is referred to as a frame. The slot is comprised of a plurality of OFDM symbols.
FIG. 10 shows an example of the structure of a downlink communication frame, and the frame is comprised of nine slots in the time-axis direction and twelve slots in the frequency-axis direction. When a base station performs radio data communications to mobile stations, the base station is capable of allocating slots forming a frame to respective different mobile stations to transmit data, or also capable of allocating all the slots to a single mobile station to perform radio communications.
Non-patent Document 1 shows the OFDM communication scheme proposed by 3GPP. Such a communication method is studied in Non-patent Document 1 that as a downlink transmission form, one communication zone with slots divided in the frequency direction and the time direction is used efficiently by a plurality of mobile stations to enhance communication efficiency of the entire cell. Proposed as the downlink radio communication scheme are a communication method for combining a plurality of modulation schemes, coding rates and spreading ratios, allocating each slot to a mobile station with good propagation path conditions by a scheme corresponding to propagation path conditions of each mobile station to perform radio communications, and obtaining the multi-user diversity effect to enhance throughput of the entire cell, and another method for using the whole or part of frequency bandwidth when propagation path conditions deteriorate or the moving speed of a mobile station is fast, using subcarriers of a higher number of frequency bands, and thereby obtaining the effect tolerant to fading i.e. frequency diversity effect.    Non-patent Document 1: NTT DoCoMo “3GPP R1-050590 Physical Channels and Multiplexing in Evolved UTRA Downlink” Jun. 16, 2005, p. 6-11